The present invention relates to industrial processes. More specifically, the invention relates to industrial process field devices for use in monitoring or control of industrial processes.
In many industrial process environments, combustible atmospheres are present in the environmental space surrounding industrial transmitters. A high power spark from connection or disconnection of a battery has a potential to ignite the combustible atmosphere.
In many industrial process environments, corrosive dust, liquids or mists are present which can damage electronic circuitry. Electronic circuitry is typically enclosed in a sealed electronic compartment. However, when such compartments are opened to replace a battery and then resealed, there is a potential to contaminate battery contacts or to seal corrosive chemicals inside the electronics compartment causing long term degradation of the electronics. On the other hand, batteries installed outside the transmitter housing are also subject to corrosion.
Circuits inside a transmitter typically carry enough electrical energy to spark and ignite a combustible atmosphere under accidental short circuit or fault conditions. Special precautions are thus taken before opening a transmitter electronics compartment. Either the surrounding environment is cleared of combustible vapors, the cable providing power to the transmitter is deenergized, or both. To increase safety, organizations require “hot work permits” and specially trained personnel before a transmitter is opened in an area where combustible atmospheres are sometimes present.
In many industrial process environments, there is severe vibration of pipes and tanks upon which transmitters are mounted. Ordinary battery connectors such as clips and snaps can shake loose in such an environment causing the transmitter to stop functioning.
Modern replaceable cells and batteries typically have a relatively high mass. Under high vibration conditions, the forces on the battery due to acceleration are significant, and cracking can take place in battery mounting structures, particularly when such structures are formed of plastic resin. Any relative motion in the battery connection will eventually cause wear and could lead to failure.
While cells and batteries can provide low current levels under ordinary operating conditions, batteries and cells typically produce very high short circuit currents under fault conditions. A typical fault condition is a short circuit in a circuit that is external to the cell or battery. In addition, cells and batteries have a large energy storage capacity or equivalent electrical capacitance C. The high short circuit currents under fault conditions and the large energy storage capacity are typically incompatible with intrinsically safe circuit specifications. It is thus difficult to mount cells or batteries outside from the transmitter housing and run a battery cable through a combustible atmosphere between the transmitter and the battery. Such a battery cable would typically violate intrinsically safe circuit requirements.
Similar difficulties are encountered with other types of battery powered industrial process field devices. A method and apparatus are needed for providing battery powered industrial process field devices that have a wide range of applicability in industrial process environments, particularly when such environments include a combination of combustible atmospheres, corrosive chemicals and vibration.